The Westminster Quarters, from its use at the Palace of Westminster, is a melody used by a set of four quarter bells to mark each quarter-hour. It is also known as the Westminster Chimes, Cambridge Quarters, or Cambridge Chimes, from its place of origin, the Church of St Mary the Great, Cambridge.

The Westminster Quarters are sounded by four quarter bells hung around Big Ben in the Elizabeth Tower belfry, in the Palace of Westminster. These are:

The quarters consist of five changes, permutations of the four pitches provided by these quarter bells (G♯₄, F♯₄, E₄, B₃) in the key E major. This generates five unique changes as follows:

Each of the five changes is played as three crotchets (quarter notes) and a minim (half note) and are always played in the sequence 1, 2, 3, 4, 5. This sequence of five changes is used twice every hour as follows:

The number of changes used matches the number of quarter hours passed.

Because the five changes are used twice, and in the same sequence, the mechanism that trips the hammers needs to be programmed with only five changes instead of ten, reducing its complexity.

Both the third quarter and the full hour require the fourth quarter bell, B₃, to be rung twice in quick succession (changes 4,5,1 and 2,3,4,5); too quick for the hammer to draw back for the second strike. To address this, the fourth quarter bell is equipped with two hammers on opposite sides and becomes, effectively, a fifth bell for the mechanism to play.

The first and third quarters finish on the dominant, B, while the half and full hours finish on the tonic, E, producing the satisfying musical effect that has contributed to the popularity of the chimes.